1. Field of the Invention
Embodiments of the present invention relate to a drawing apparatus configured to perform drawing on a substrate with a plurality of charged particle beams.
2. Description of the Related Art
As one example of the drawing apparatuses, a multi-column drawing apparatus is known in which a projection unit is provided for each of the charged particle beams (see Japanese Patent Application Laid-Open No. 09-007538). Since projection units are provided independently, such a drawing apparatus does not have a crossover on which all of the charged particle beams converge. Thus, the influence of a coulomb effect is small, and such a drawing apparatus may effectively increase the number of charged particle beams.
However, in order to increase the number of charged particle beams in the multi-column drawing apparatus, it is generally necessary to increase the divergence angle (divergence half angle) of a charged particle beam from a charged particle source in an irradiation optical system which is located on the front side of the plurality of projection units. When the divergence angle of a charged particle beam from the charged particle source increases, the charged particle beams irradiated on the plurality of projection units are not easily made parallel sufficiently due to the aberration of the irradiation optical system. As a result, the irradiation angle (incidence angle) becomes non-uniform. Eventually, the non-uniformity of the irradiation angle causes non-uniformity of properties between the charged particle beams. However, there is an issue associated with the aberration of the irradiation optical system.